/// <summary>
/// Approximate a cubic Bezier curve with a spline of n quadratics.
/// </summary>
/// <param name="curve">The four vectors representing the control points of the cubic Bezier curve</param>
/// <param name="maxError">Permitted deviation from the original curve</param>
/// <param name="spline">A list of 2D tuples, representing control points of the quadratic
/// spline if it fits within the given tolerance, or null if no
/// suitable spline could be calculated</param>
/// <returns>True if the curve could be converted, else false</returns>
internal static bool CurveToQuadratic(CubicCurve curve, float maxError, out Complex[] spline)
{
spline = null;
for (var n = 1; n < MaxN + 1; n++)
{
if (CubicApproximateSpline(curve, n, maxError, out spline))
{
return(true);
}
}
return(false);
}
/// <summary>
/// Approximate a cubic Bezier with a single quadratic within a given tolerance.
/// </summary>
/// <param name="controlPoints">Four complex numbers representing control points of the cubic Bezier curve.</param>
/// <param name="maxError">Permitted deviation from the original curve.</param>
/// <param name="quadraticCurve">Three complex numbers representing control points of the quadratic
/// curve if it fits within the given tolerance, or null if no suitable
/// curve could be calculated.</param>
/// <returns>True if the curve could be converted, else false</returns>
private static bool CubicApproximateQuadratic(CubicCurve controlPoints, float maxError, out QuadraticCurve quadraticCurve)
{
if (!TryCalculateIntersection(controlPoints.Point0, controlPoints.Point1, controlPoints.Point2, controlPoints.Point3, out var q1))
{
return(false);
}
var c0 = controlPoints.Point0;
var c3 = controlPoints.Point3;
var c1 = c0 + (q1 - c0) * TwoOverThree;
var c2 = c3 + (q1 - c3) * TwoOverThree;
if (CubicFarthestFitsInside(0, c1 - controlPoints.Point1, c2 - controlPoints.Point2, 0, maxError))
{
return(false);
}
quadraticCurve = new QuadraticCurve(c0, q1, c3);
return(true);
}
// Cubic bezier curve
public void Curve4(float x1, float y1, float x2, float y2, float x3, float y3)
{
var curve = new CubicCurve(
new Complex(lastX, lastY),
new Complex(x1, y1),
new Complex(x2, y2),
new Complex(x3, y3)
);
if (!CubicToQuadraticConverter.CurveToQuadratic(curve, 1, out var spline))
{
throw new Exception("Couldn't create a spline from the bezier curve");
}
for (var i = 0; i + 2 < spline.Length; i += 2)
{
var p1 = spline[i + 1];
var p2 = spline[i + 2];
Curve3((float)p1.Real, (float)p1.Imaginary, (float)p2.Real, (float)p2.Imaginary);
}
}
/// <summary>
/// Approximate a cubic Bezier curve with a spline of n quadratics.
/// </summary>
/// <param name="curve">The four complex numbers representing control points of the cubic Bezier curve.</param>
/// <param name="n">Number of quadratic Bezier curves in the spline.</param>
/// <param name="maxError">Permitted deviation from the original curve.</param>
/// <param name="spline">A list of `n+2` complex numbers, representing control points of the
/// quadratic spline if it fits within the given tolerance, or null if
/// no suitable spline could be calculated.</param>
/// <returns>True if the curve could be converted, else false</returns>
private static bool CubicApproximateSpline(CubicCurve curve, int n, float maxError, out Complex[] spline)
{
spline = null;
if (n == 1)
{
if (CubicApproximateQuadratic(curve, maxError, out var quadraticCurve))
{
spline = new Complex[] { quadraticCurve.Point0, quadraticCurve.Point1, quadraticCurve.Point2 };
return(true);
}
}
var cubics = SplitCubicIntoNIterations(curve.Point0, curve.Point1, curve.Point2, curve.Point3, n).ToArray();
// Calculate the spline of quadratics and check errors at the same time
var nextCurve = cubics[0];
var nextQ1 = CubicApproximateControl(0, nextCurve.Point0, nextCurve.Point1, nextCurve.Point2, nextCurve.Point3);
var q2 = curve.Point0;
var d1 = Complex.Zero;
var splineTemp = new List <Complex> {
curve.Point0, nextQ1
};
for (var i = 1; i < n + 1; i++)
{
// Current cubic to convert
var(_, c1, c2, c3) = nextCurve;
// Current quadratic approximation of current cubic
var q0 = q2;
var q1 = nextQ1;
if (i < n)
{
nextCurve = cubics[i];
nextQ1 = CubicApproximateControl(i / (n - 1), nextCurve.Point0, nextCurve.Point1, nextCurve.Point2, nextCurve.Point3);
splineTemp.Add(nextQ1);
q2 = (q1 + nextQ1) * 0.5f;
}
else
{
q2 = c3;
}
// End-point deltas
var d0 = d1;
d1 = q2 - c3;
var f1 = q0 + (q1 - q0) * TwoOverThree - c1;
var f2 = q2 + (q1 - q2) * TwoOverThree - c2;
if (Complex.Abs(d1) > maxError || !CubicFarthestFitsInside(d0, f1, f2, d1, maxError))
{
return(false);
}
}
splineTemp.Add(curve.Point3);
spline = splineTemp.ToArray();
return(true);
}
